1. Field of the Invention
This invention relates to an inlet for an aircraft engine, and more particularly to a variable camber inlet for a supersonic aircraft engine.
2. Discussion of the Prior Art
Modern jet-powered aircraft that are built to fly at supersonic speeds usually incur problems at subsonic speeds. The aircraft suffer a severe penalty in efficiency due to the sizing of the air inlets to the engine. The capture area of the air inlet must be made large enough to supply the amount of air required by the engine for supersonic operation. At the lower subsonic cruise flight condition, a large capture area is not required to meet the demands of the engine. The excess airflow spills around the air inlet and results in a drag penalty. The increase in drag reduces the effective range of the aircraft, and inhibits its ability to carry out a given mission.
The prior art discloses the basic concept of providing aircraft engine inlets with a variable camber leading edge to accommodate various flight conditions and provide efficient operation during subsonic operation.
A search of the prior art relating to the particular field of the invention discovered the following United States patents:
______________________________________ Reference Inventor(s) Issue Date Classification ______________________________________ (1) 2,934,288 MacINTYRE 4-26-60 244/44 (2) 3,074,232 SOYER 1-22-63 244/44 (3) 3,494,380 MARTIN 2-10-70 137/15.1 (4) 3,532,129 WARD, et al. 10-6-70 137/15.1 (5) 3,589,379 DAVES, et al. 6-29-71 137/15.1 (6) 3,611,724 KUTNEY 10-21-71 137/15.1 (7) 3,618,699 EVANS, et al. 11-9-71 137/15.1 (8) 3,659,418 POUCHER, et al. 5-2-72 137/15.1 (9) 3,664,612 SKIDMORE, et al. 5-23-72 244/53 (10) 3,763,874 WILDE, et al. 10-9-73 137/15.1 ______________________________________
References (1) through (4), and (6) through (10) apply to relatively low speed operation of subsonic aircraft. References (1), (2), (3), (6) and (7) disclose inflatable devices for varying camber in an aircraft engine useful in subsonic aircraft. Reference (8) discloses a device for improved diffuser efficiency by the use of wall vortex flow, and has no similarity in function or structure to the present invention. Reference (4) discloses a device to reduce the throat area of a subsonic aircraft inlet at low speeds, such as during approach, landing and taxi. The objective of this invention is noise reduction due to choking the flow of air through the engine throat. Further, the device is disclosed for use with a circular inlet, and not a rectangular inlet.
Reference (10) discloses a mechanical device for increasing the contraction ratio of the inlet lip. This device corrects the problems of distortion due to cross-wind operation of a subsonic aircraft inlet at very low speeds such as during takeoff, landing and taxi. The device does not teach utility at supersonic speeds.
Reference (9) discloses a variable highlight inlet for an aircraft engine. This invention applies to only circular inlets and limits its teachings to subsonic conditions.
In reference (5), U.S. Pat. No. 3,589,379, Daves, et. al., a complete inlet duct for a supersonic aircraft is disclosed. The inlet duct incorporates a rocking ramp on its upper forward edge. The rocking ramp pivots about a center point to provide a variation in the ratio of inlet capture area to throat area. The purpose of the ramp is to reduce the inlet throat area at supersonic speeds. A ramp is not attached to the lower forward edge as in the present invention. Further, the ramp disclosed in U.S. Pat. No. 3,589,379 is a solid structure which does not change its shape during pivoting, and lacks correct external aerodynamic shape which provides good streamline matching for all flight regimes.